Transistorized control system



g- 3, 1965 L. R. LEASE 3,198,962

TRANSTSTORIZED CONTROL SYSTEM Filed Oct. 22, 1962 2 sheets sheet 1 BASE2 I I8 9 I3 352%; MW l9 s -.o. MC. W H4; m

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L E Z q Ag SENSING COIL EX C TER FIELD I NVEN TOR. LEON R. LEA 85 FIG. 39%R'2UMM ATTORNEYJ United States Patent [all 3,18,9-52 TRANSESTGREZEDCGNTRQL SYSTEM Leon R. Lease, Manlrato, Winn assignor to Electra)!Equipment, Inc, a corporation oft Minnesota Filed Get. 22, 1962, Ser.No. 2392,1436 11 Claims. (Cl. 307-885) This invention relates totransistorized control systems and particularly to systems including apower transistor controlled through the use of contacts. Specifically,the present invention relates to transistorized control systemsincluding switch means with one normally open pair of contacts and onenormally closed pair of contacts in a single pole-double throwarrangement for controlling a power transistor, this basic system beingadapted to use in many and varied specific electrical applications.

The present invention provides a control means for switching directcurrent by means of a transistor through the use of contacts,specifically in a single pole-double throw arrangment. The basicstructure of the control system of the present invention provides ameans for switching the power to inductive, resistive or capaacitiveloads, or a combination thereof, without directly having to make orbreak the set current providing the power to said load, by means ofswitch contacts whether a direct switch or a relay switch and whethermanually, mechanically, electrically or hydraulically operated.

The system of the present invention makes possible the switching ofhigher currents than would normally be permissible for the particularcontacts used as provided by good practice, thereby eliminating contacterosion due to sparking and much of the radio interference caused bysparking when said currents are switched directly with contacts. A powertransistor in a switching mode is controlled in such a way that theswitch contacts cannot establish or maintain an are thereby eliminatingradio interference and contact erosion and greatly enhancing theserviceable life of the control means.

The basic circuit of the control system of the present invention isuseful, for example, in generator voltage regulators where thetransistorized control circuit is employed to switch the generatorexciter field current so that the generator voltage is controlled in apredetermined manner, most generally at an essentially constant level.

Another use of the basic control circuit is in generator .voltageregulators where the generator field current is controlled by thetransistorized circuit to control the output voltage or" the generatorin a predetermined fashion, generally at an essentially constant level.

A still further use of the control system circuit is in th outputcurrent control of generators where the output current of the generatoris controlled in a predetermined fashion, generally at a constant level,or, in the case of a D.C. generator, the output current is controlled ateither on or oil or in between at any level between on and off.

The control circuit is useful as a regulating element of regulated DC.power supplies whether used to control the voltage at a predeterminedlevel, or to control the current at a predetermined level, or acombination of the two.

Still another application of the control circuit of the presentinvention is as a control element in a battery charger for maintaining abattery at full charge. The control circuit may be so used whether thebattery charger is of the transformer-rectifier type or is a rotatingbattery charger.

The control circuit may be used in the control of the field of directcurrent motors to maintain the motor speed generally at a constantlevel. The same means of control is useful in the armature of directcurrent motors for the control of the motor speed.

The control circuit is useful for controlling the speed of universalmotors run ofi direct current in full on or off condition or anyintermediate condition.

The control circuit is useful in the switching of large or small amountsof direct current under circumstances where the voltage and currentwould likely cause arcing with normal DC. relays.

The control circuit is useful for the transistorizing of the ignitionsystems of automobiles to give the points indefinite lite.

The structure of the control system circuit and its versatility in meansof control are shown in the accompanying drawings in which the samenumerals refer to corresponding parts and in which:

FIGURE 1 is a single pole-double throw switch operated circuit includinga PNP transistor;

PEGURE 1A is a similar circuit including an NPN transistor;

FEGURE 2 is a simple electromagnetic sensing operated circuit;

FIGURE 3 is an electromagnetic senser with D.C. feed backs operatedcircuit; and

FiG-URE 4 is an electromagnetic senser with A.C. feed backs operatedcircuit.

As shown in FIGURES 1 and 1A, the transistorized control circuit in itssimplest form comprises a PNP transistor, indicated generally at 10, oran NPN transistor, indicated generally at 13A, each including an emitterll, collector l2 and base 13, inserted in a power line 14 which alongwith line 15, extends from a source of electrical power or input to anoutput or load, which may be any'of a variety of devices for absorbingor converting the power from the power source.

A single pole-double throw switch including normally open contacts 16and normally closed contacts 17 is provided, with the common terminal ofthe contacts connected to the base lead of the transistor, the otherterminal of the normally open contacts connected to the emitter lead ofthe transistor and the other term nal of the normally closed contactsconnected to the collector lead of the transistor. The contacts may bethose of a direct switch or a relay switch, whether manually,mechanically, electrically or hydraulically operated.

A resistor 18 is connected between the emitter and base across theterminals of normally open contacts 16 and a resistor 12* is connectedbetweenthe base and collector across the terminals of normally closedcontacts 17.

When the normally closed contacts 17 are such that the base 13 tocollector 12 is shorted, the transistor is in the saturated condition atfull turn on where the base to emitter voltage is generally in theneighborhood of 0.2 volt, although this voltage may vary between about0.1 to 0.5 volt. When both contacts are open during the operation of theswitch, the ratio of the resistor 18 between the emitter i1 and base 13,to the resistor 19 between the base 13 and the collector 12 determinesthe percentage of turn on. This should, in general, be between about 10%and 40% of full turn on.

When the normally open contact 16 becomes closed, the emitter 11 to base13 is shorted. Consequently, that potential is at zero and thetransistor becomes fully turned off and the only current that can flowat that time is the current flowing through the resistor 19 connectedbetween the base 13 and collector 12. This, in general, will be in therange of milliamperes. Thus, using a simple single pole-double throwswitch enables the transistor to be turned fraorn full on to partiallyon to full off in a three step operation in which the contactsswitchvery little power.

In general, the emitter to base voltage when the transistor is in thenormally saturated condition will be ape proximately 0.20 volt and whenboth contacts are open there will be approximately 0.35 volt between theemitter and base. Assuming that the entire base current, which isgenerally less than 100 milliamps, is switched from 0.35 volt to 0.20volt, or a difference of 0.15 volt, a total power of 0.015 watt isswitched. The potential at which these contacts have to open, and thecurrent through them, are not sufiicient to maintain or establish an arcwith the result that radio interference due to sparking and erosion, orcontact wear due to sparking, is virtually eliminated.

As shown in FIGURE 2, most applications in which the control circuit ofthe present invention is used in corporate an electromagnetic sensingelement which in turn activates the contacts, which in turn control thetransistor. Thus, in FIGURE 2, there is shown a simple electromagneticsensing operated circuit in which the normally open contacts 16A andnormally closed contacts 17A may be those of a relay. The contacts 16Aand 17A are operated in response to an electromagnetic sensing coil 29,which may be a relay coil, having sensing leads 21 and 22. The sensingcoil may be connected from positive to negative, across the load, or itmay have completely separate sensing.

When the control circuit is used in conjunction with an electromagneticsensing element in a circuit as a regulator for a generator, forexample, the normally closed contacts 17A drive the transistor into fullturn on. The current through the transistor, and consequently throughthe field of the generator which is in series with the transistor,remains at full value until the voltage rises to its nominal value. Thenominal value is pre-set at the point where the electromagnetic sensingelement will activate the contacts.

At nominal voltage, the contacts 17A that normally short the base to thecollector open, and the ratio of the two resistors 18 and 19 connectingthe emitter to the base and the base to the collector across thetransistor determines the ratio of turn on, which should be betweenabout to 70% and more generally between about and 40%. This immediatelycuts back the field to between 5% to 70%, or about 10% and 40%. If thisis still too high, so that the generator voltage rises above the nominalvalue, the contacts 16A connecting the base to the emitter closeshorting these two points and bringing the base potential to that of theemitter. This consequently turns otf the transistor fully.

The only field current that is then available must go through theresistor 19 connecting the base to the collector. This, in general, is ahigh valued resistor which would normally allow only milliamperes ofcurrent to flow, as compared to the amperes required for full voltage onthe generator.

When the current on the field is reduced to essentially zero, as happenswhen the emitter is shorted to the base, voltage must drop until it goesback to normal at which time the contacts 16A shorting the emitter tothe base open again and allow from 10% to 40% of the current to fiowonce more. If this is not sufiicient to energize the generator tonominal voltage, the voltage would drop further, at which point thecontacts 17A shorting the base to the collector close and allow fullpotential to be applied to the field momentarily. This in turn causesthe gem erator voltage to rise once more at which point the con tacts17A open and the cycle is repeated.

Essentially, this causes a modulation of the generator voltage over anarrow band such that the contacts can be operated in sequence. Thepoint where the normally closed contacts 17A open is a lower voltagethan the point where the normally open contacts MA close. Consequently,there will be a modulation of that generator voltage, which in turn isapplied to the electromagnetic senser between these two points asdetermined by the sensitivity of the senser. The control of thegenerator voltage is accomplished by the rapid switching at a rate ofhundreds of times per second of the generator field cur- Itint'Or theexciter field current, as the case may be, from a condition of full turnon to part turn on to zero turn on, or between any two of these threesteps.

The principal advantage is that the electromagnetic senser causes thetransistor to operate in two or more of these conditions hundreds oftimes each second. Consequently, the regulator is many times faster thanis the time constant of the generator where it would ordinarily be used.This rapid regulator response and its ability to turn fully on will giveexceptionally fast recovery of generator voltage on the application ofload. Its ability to turn fully ofi will give similarly fast recovery ofvoltage on load rejection. Modulation of the generator voltage envelopeis minimized by the extremely fast-sensitive senser. Life is indefiniteas the transistor, and not the contacts, switch tie field current.Consequently, the normal inductive load of the generator or exciterfields cannot cause an arc and create radio interference or contacterosion reducing contact life.

A further advantage of the control system of the present invention isthat as ambient temperature increases, the field requires more voltageand consequently absorption requirements placed on the transistor areless. Further, as the temperature of the transistor rises, the forwarddrop of the transistor becomes lower allowing the required field currentto flow with even less transistor absorption at the higher ambienttemperature.

Another major advantage of the control system is that the gain of thetransistor increases with increasing temperature which gives thetransistor the effect of being more nearly at full turn on and full turn05. This also reduces the absorption requirement of the transistor athigher ambient temperatures. Since the transistor operates in aswitching mode during which it is operating a large percentage of thetime at either full turn on or full turn off it is capable of handlingseveral times the normal power capabilities of the transistor. In otherwords, in the case of a normal watt transistor at 25 C. casetemperature, it is possible that by keeping the case temperature at 25C. switching in the neighborhood of 700 to 1,000 watts may beaccomplished. Even where the case temperature rises and the powerdissipation consequently goes down, the system is still capable ofswitching several times the normal power dissipation of the transistor.

In FIGURE 3 there is shown a control circuit operated by anelectromagnetic senser with D.C. feed-back in connection with a voltageregulator. Terminals 1, 2, 3, 4 and 5 are those of the regulator,terminals 1 and 2 being connected to the exciter field. Transformer T-lis a sensing transformer which reduces volts AC. to 12 volts A.C.Rectifiers CR]. and CR-2 are sensing recti fiers which change 12 voltsAC. to 12 volts D.C. Rectifier CR-S protects transistor 10 againstinverse voltage spires. Rectifier CR-'-4 allows current to flow whentransistor 10 is in off position. Windings 23 and 24 are feed-backwindings on electromagnetic senser 20. Contacts 16A and 17A are thenormally open and normally closed contacts, respectively, which areresponsive to the electromagnetic senser. Resistors 1S and 19 are thebias resistors for transistor 10.

In FIGURE 4 there is shown a control circuit operated by anelectromagnetic senser with AC. feed-back in connection with a generatorvoltage regulator of a vehicle. The regulating and control portion ofthe circuit is indicated within broken line boxes 25 and 25A. Terminals1, 2, 3, 4 and 5 are the terminals of the regulator, terminal 1 beingfor connection to the positive pole of the vehicle battery, terminal 2being for connection to the negative pole of the battery, terminal 3being for connection to the ignition coil of the vehicle and terminals 4and 5 being for connection to the exciter field. Normally open relaycontacts K2 are activated by power to the vehicle ignition coil.Rectifiers CR1(2) and Cit-1(3) are power rectifiers; rectifiers CR1(1)and CR1(4) are sensing and power rectifiers; and rectifiers CR-Z andCR-S are sensing rectifiers. The sensing rectifiers change A.C. to D.C.for the electromagnetic sensor 20. Winding 26 is a feed-back winding onelectromagnetic senser 20. Low (12 volts A.C.) voltage is supplied bythe generator. Higher (110 volts A.C.) voltage is supplied to thereceptacles. Frequency sensitive circuit 27 indicates if frequency isabove 60 cycles, at 60 cycles, or below 60 cycles.

According to the present invention the switch means controls thetransistor as distinguished from prior art circuits in which thetransistor controls a relay or other switch means. The actual powerswitching is accomplished by the transistor, and not the switch meanscon tacts, nor do the contacts conduct the major portion of current.

It is apparent that many modifications and variations of the inventionas hereinbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

I claim:

1. A control system including a transistor and a single pole-doublethrow switch means, one of the pairs of contacts of said switch meansbeing normally open and the other pair of contacts being normallyclosed, the common terminal of said pairs of contacts of said switchmeans being connected to the base of said transistor, the other terminalof one of said pairs of contacts being connected to the emitter of saidtransistor and the other terminal of the other of said pairs of contactsbeing connected to the collector of said transistor, a first resistorconnected between the emitter and base of said transistor and anotherresistor connected between the base and collector of said transistor.

2. A control system according to claim 1 further characterized in thatsaid switch means are electromagnetically actuated and said systemincludes an electromagnetic sensing element.

3. A control system according to claim 2 further characterized in thatsaid switch means are relay contacts and said sensing element is a relaycoil.

4. A control system according to claim 1 further characterized in thatthe ratio of said first resistor to said other resistor is such thatwhen both pairs of contacts are open current flow is about 5% to 70% offull current flow.

5. A control system according to claim 1 further characterized in thatsaid transistor, switch means and resistors are connected in a powerline between a power source and load to be acted upon by said powersource, the emitter of said transistor being connected to said powersource and the collector of said transistor being connected to saidload.A

6. A control system according to claim 1 further characterized in thatsaid normally open contacts of said switch means are connected betweenthe emitter and base or" said transistor and said normally closedcontacts are connected between the base and collector of saidtransister.

'7. A control system including a transistor and a single pole-doublethrow switch means, said switch means including one normally open pairof contacts and one normally closed pair of contacts, said switch meansincluding one terminal common to both pairs of contacts, said commonterminal being connected to the base of said transistor, the otherterminal of said normally open contacts being connected to the emitterof said transistor, the other terminal of said normally closed contactsbeing connected to the collector of said transistor, a first resistorconnected between the emitter and base of said transistor and anotherresistor connected between the base and collector of said transistor.

8. A control system according to claim 7 further characterized in thatsaid switch means are electromagnetically actuated and said systemincludes an electromagnetic sensing element.

9. A control system according to claim 8 further characterized in thatsaid switch means are relay contacts and said sensing element is a relaycoil.

10. A control system according to claim 7 further characterized in thatthe ratio of said first resistor to said other resistor is such thatwhen both pairs of contacts are open current flow is about 5% to of fullcurrent flow.

11. A control system according to claim 7 further characterized in thatsaid transistor, switch means and resistors are connected in a powerline between a power source and load to be acted upon by said powersource, the emitter of said transistor being connected to said powersource and the collector of said transistor being connected to saidload.

References Cited by the Examiner UNITED STATES PATENTS 2,763,832 9/56Schockley 307-885 3,112,410 11/63 Schmid 307-885 ARTHUR GAUSS, PrimaryExaminer.

1. A CONTROL SYSTEM INCLUDING A TRANSISTOR AND A SINGLE POLE-DOUBLETHROW SWITCH MEANS, ONE OF THE PAIRS OF CONTACTS OF SAID SWITCH MEANSBEING NORMALLY OPEN AND THE OTHER PAIR OF CONTACTS BEING NORMALLYCLOSED, THE COMMON TERMINAL OF SAID PAIRS OF CONTACTS OF SAID SWITCHMEANS BEING CONNECTED TO THE BASE OF SAID TRANSISTOR, THE OTHER TERMINALOF ONE OF SAID PAIRS OF CONTACTS BEING CONNECTED TO THE EMITTER OF SAIDTRANSISTOR AND THE OTHER TERMINAL OF THE OTHER OF SAID PAIRS OF CONTACTSBEING CONNECTED TO THE COLLECTOR OF SAID TRANSISTOR, A FIRST RESISTORAND ANOTHER RESISTOR CONNECTED BETWEEN THE BASE AND COLLECTOR OF SAIDTRANSISTOR.